(() => {
    "use strict";

    // -------------- DIGITS FOR GIVEN BASE --------------

    // showIntAtBase :: Int -> (Int -> Char) ->
    // Int -> String -> String
    const showIntAtBase = base =>
        // A string representation of n, in the given base,
        // using a supplied (Int -> Char) function for digits,
        // and a supplied suffix string.
        toChr => n => rs => {
            const go = ([x, d], r) => {
                const r_ = toChr(d) + r;

                return 0 !== x ? (
                    go(quotRem(x)(base), r_)
                ) : r_;
            };

            const e = "error: showIntAtBase applied to";

            return 1 >= base ? (
                `${e} unsupported base`
            ) : 0 > n ? (
                `${e} negative number`
            ) : go(quotRem(n)(base), rs);
        };

    // ---------------------- TEST -----------------------
    const main = () => {
        // showHanBinary :: Int -> String
        const showHanBinary = n =>
            showIntAtBase(2)(
                x => "〇一" [x]
            )(n)("");

        return [5, 50, 9000]
            .map(
                n => `${n} -> ${showHanBinary(n)}`
            )
            .join("\n");
    };


    // --------------------- GENERIC ---------------------

    // quotRem :: Integral a => a -> a -> (a, a)
    const quotRem = m =>
        // The quotient, tupled with the remainder.
        n => [Math.trunc(m / n), m % n];


    // MAIN ---
    return main();
})();